One of the fascinating problems in biochemistry is to determine how subtle changes in related molecules cause drastic changes in their biochemical behavior. An example of this structure function problem is the role of similar high=valent porphyrin intermediates in the different reactions catalyzed by hydroperoxidate and cytochrome p-450 enzymes.Hydroperoxidases are hemoproteins with essential roles in the catabolism of toxic peroxides. Cytochrome p-450 is a monooxygenase with essential metabolic functions dealing with drug metabolism, chemical carcinogenesis, membrane detoxification and biosynthesis. The short term goal of this project is to encourage students to pursue graduate studies in the health sciences by providing a summer research opportunity to the investigators undergraduate biochemistry majors. A long term goal of this project is to increase the investigators fundamental chemical understanding of the role of high-valent porpyhrins in biological systems. This project involves the use of novel techniques in quantum chemistry to study the magnetic and electronic structure of high-valent porphyrin n- cation radicals found at the active site of oxygen activation enzymes. The primary goal of this research is to understand the nature of spin-coupling in these systems, and to explore how these couplings influence their observed spectral and catalytic properties. This will be accomplished by calculations on Heisenberg coupling constants, Mossbauer and magnetic resonance parameters (including g and hyperfine tensors), electronic transition dipoles, and charge densities as a function of systematic variations in active site geometries.All calculations will use Xalpha or local spin density effective potentials. Systems to be studied include: (a) ferryl oxygen intermediates which function as the active catalytic agent in peroxidase, catalase, and cytochrome p-450 enzymes; and (b) planar and ruffled synthetic tetraphenyl porphyrins which serve as models for spin coupling in hemoproteins. Models for these systems will be used to interpret experimental magnetic measurements on these systems.